Failures to index a document are not noticed

Spotted while working on https://gitlab.com/gitlab-org/gitlab-ee/merge_requests/9760#note_152129715

We changed the mapping type from dynamic to strict. I checked whether the indexing failed or succeeded - gitlab-elasticsearch-indexer succeeded. What I didn't notice immediately was that only a few thousand (rather than 262,000) documents had been created.

I think that when elasticsearch rejects a document, gitlab-elasticsearch-indexer just doesn't notice. Adding the two missing type fields got the index size back up to 262K documents on a reindex.

This one's pretty bad, so I'm marking it ~S2 @jramsay @smcgivern @DouweM @mdelaossa